This practice has some interesting historical antecedents. The main species of nitrogen in mammal urine is urea (H2N-C-NH2), but the ideal form of nitrogen for fertilizer is probably nitrate (NO3-) in most cases (and it's easier to store and transport as a solid). Soil bacteria in healthy soils around roots will also transform urea to ammonia and nitrate in fairly complicated processes, and there are pH effects. For an overview:
However, nitrate has many other practical uses, and in industrial Europe before the invention of Haber-Bosch, a major use was gunpowder manufacture (the ingredient saltpeter, potassium nitrate KNO3). An entire industry existed, based on taking animal and human urine (and other materials, like rotting animal carcasses) and processing it in a certain manner to encourage its conversion to nitrate crystals, typically involving beds of wood chips which would become covered with a frost of potassium nitrate crystals. The British government passed laws about the storage of urine for the king's 'petermen' to come and collect for this purpose. Here's a technical manual from 1862 on the process, from start to pure potassium nitrate (which in turn, could be converted to the important industrial chemical, nitric acid):
Fertilizers can be more than urea, like ammonium nitrate. Urea is also used, although many times it is treated for controlled release. Apart from that, some math is in order.
Let's say I need 200 kg/ha of a 12-6-6 NPK fertilizer for post-sowing 10 ha of some crop, like corn. (This is a little short of 180 lb/ac for a total of ~25 acres. I'm in Europe, and I don't know what would be a typical value for the US).
This fertilizer has 12% w/w of total nitrogen, so for the total area my needs are 240 kg of nitrogen (~530 lb).
An adult will produce an average of 1,4 L (0.37 gal) of urine daily, with a nitrogen content of 8,83 g/L, so this means a total of 12,36 g/day, or 4,5 kg/year (~10 lb/year).[1]
So I'll need the urine that 53 people pee for a whole year for this single crop. A six tower pivot has something around 4 or 5 times that area. And this area can be used twice a year for different crops. The average US farm has 445 ac.[2]
> Fertilizers can be more than urea, like ammonium nitrate
... which you have to keep locked up, because terrorists. Usually they're smart enough to avoid hanging around in rusty white Ford Transits with Irish plates, but you'd probably not be too surprised to see the numbers on that.
All fertilizers and pest control products are locked up. And each year I have to give the government proof of fertilizer usage, with up to date inventories, invoices and fertilization tables for all crops that used solid fertilizers. I also have to sign terms of responsibility provided by the suppliers.
I had some stuff stolen in the past, but never fertilizer.
The average yield for corn in the US for 2021 was 176.5 bu/ac. This is around 11,9 ton/ha. For 10 ha, a total of 119 ton.[1][2]
How many people this would feed is hard to tell, because it depends on the kind of corn. Some corn is meant for human consumption, some other for livestock feed (which in turn is meant for human consumption. But as a rough estimate one can add these two to find an order of magnitude.
In 2008, the USDA broke down the usage for maize, with 133,4 Mton (5250 Mbs) for livestock and 8,3 Mton (327 Mbs) for human consumption. That year, the US population was around 303.5 million people, so that gives an average of 467 kg (1030 lb) a person each year.[3][4]
So those 10 ha would produce enough corn for 240 people for a whole year.[5]
This comment might come a little bit too late, but I wouldn't want to give the impression that these numbers suggest using urine as fertilizer is self-sustainable. It is not self-sustainable, and it might not be sustainable in the long term. For many reasons:
- First of all, urea as a fertilizer is not completely effective, because some of it will be drained. Urea can be treated for slow release, but this requires processing. And even in this case, some of it will just be degraded by bacteria (some bacteria will turn it into compounds that plants can use, but generally urea content will fall with time).
- I used total nitrogen from urea, but in reality a part of that nitrogen does not come as urea.
- I also used average yields, which depend on the usage of more powerful fertilizers. Fertilizing with urea alone will lead to smaller yields.
Let's say that average yield woud drop to 50% and that I would need not 53 bu 80 people's yearly urine. That would mean I would only provide enough corn for 120 people each year, for a input of 80, which gives a ratio of 3:2. Seems good enough. Unfortunately this is not the case.
Human urea is the result of human diet and metabolism, which gets nitrogen from many different protein sources. Self-sustainability means that those 120 people would have to eat only corn and meat from corn-fed livestock, or trade this for other protein sources (which would only externalize this unsustainability: some other people's diet would have to change). Even if it were possible to keep up with the same urea output without severe weight loss, this would not be enough:
- First of all, plants use nutrients to grow many inedible parts, and that is an important drain of nitrogen. This also means all plants, not just the ones we eat.
- Livestock would still need food sources other than corn. The above assumptions assume well-fed cattle.
Finally, as someone already noted in another comment, human urine contains a significant amount of salt, and without its removal this could lead to excess salinization that would render the soil infertile in the long term. And the higher concentrations of urea needed could also worsen the already present problem of eutrophication.
But using urine might still be a great help with local, temporary unavailability of better fertilizers.
Not speaking for them, but I do contract work on the Pi/Arduino systems for the pasteurization process. It's all pretty straightforward technically, but I thought HN readers might be interested to know that it's making use of open source software under the hood (and might be open source at some point).
Surely an easy win would be the men's urinals. Collect all the pee, and just divert water away via a valve when the cleaning cycle is running. Maybe there is enough money in it for a company to install a system like that for free in restaurants, airports, public buildings etc.
I have something called a Venturi siphon that allows me to easily feed urine into the irrigation for my home garden. It definitely makes a difference.
I do worry about a build up of salt over time since I live in a low precipitation climate (12”/year). The article doesn’t seem to touch on that concern.
Never thought to use it for fertiliser, but urinating onto a compost heap to speed up the process of creation is pretty common. At least two of the presenters on BBC Radio 4's Gardener's Question Time do it - Bob Flowerdew and Christine Walkden.
Sounds like an interesting--although presumably not easily and quickly scalable--solution to fertilizer shortages. I am dubious about the environmental improvement. According to a meta-analysis[0], chemical fertilizers produce less ammonia emissions
> However, ammonia emissions, nitrogen leaching and nitrous oxide emissions per product unit were higher from organic systems.
Basically, chemical fertilizers are much more efficient and have more uniform distribution of nutrients.
One of my greatest memories of science class as a kid, was making saltpeter from scratch with a particularly creative teacher. First, we built a latrine and the class pee’d on straw and lime for a couple of months. Then, we boiled the straw in copper pots, poured the liquid into jars, and suspended cotton string in the jars. As the liquid evaporated, saltpeter grew as crystals on the string.
Sewage solids applied to farms are a major source of microplastic contamination,[0] likely since we currently commingle our valuable human waste with wastewater from washing machines.
Synthetic textiles cause 35% of ocean microplastics[1] (ie the largest single source), so this is not a small waste stream.
> To pasteurize the pee, it stays in the jug for at least two months before the farmer applies it
A 2 month "buffer" (beyond that needed due to crop seasonality) needs to hold a lot of pee.
This processing time can be reduced to 10 hours by adding watermelon seeds[1], which contain the enzyme urease.
If only the Romans had known this! They stored large amounts of urine (converting to ammonia) for washing clothes. For this reason, Roman laundries were legally forbidden from being located within city limits.
It looks like your account has been using HN primarily for ideological battle. Could you please not? We ban accounts that do that, regardless of their ideology, because it's not what this site is for, and it destroys what it is for.
This reads like a screed. Could you say precisely what you mean by the "green agenda"? I've never heard the petrochemical industry (which is what we're talking about, when we're talking about artificial fertilizer) called that before.
Also, Africa is a large continent. Significantly larger than North America. It stands to reason that there will always be parts that are easier and parts that are harder to perform commercial agriculture on.
It really seems like you’re choosing to not understand the GP.
The green agenda is just a blunt way of referring to all of the messaging and policy initiatives related to climate or environmental protection - as I understood it.
I don’t know why you think the petrochemical industry is synonymous with the green agenda. Does that not sound suspiciously incorrect to you?
> The green agenda is just a blunt way of referring to all of the messaging and policy initiatives related to climate or environmental protection - as I understood it.
This wasn't clear on my first read -- it sounded like they were claiming that the two are the same, which does indeed sound suspiciously incorrect (and is why I asked.)
